From this Law and Crime Network video, which may shed some light on whether she actually SPOKE to her parents about the change of plans or whether it was an electronic communication (it seems it was the latter, even though previously her mother was on film saying Chelsea had called them).
It's worrisome to me that if they only communicated electronically, that may not have been her at all speaking with them. And wouldn't she have known prior to the day of the flight that her pet wasn't allowed on the plane?
Her mother reported:
"She was going to fly home for the wedding in NY
but the day she was supposed to get on the airplane, she emailed Steve and said she was going to drive across country instead. So that was on the 24th."
Her father said "a change of plans last minute was NOT out of character for her. She had adopted the bearded dragon and didn’t want to come without it, but you can’t bring it on the plane. So that, ostensibly, was the reason", he said.
Her mother said: "A few days later - we were texting back and forth with her and she said “I’ve driven for 3 days and I’m in Arizona. I'm not gonna make it to the east coast for the wedding. I think I'm gonna skip the wedding, stop here for a day or two and do some camping.”"